The present invention relates generally to hydraulically actuated diaphragm pumps. More particularly, the present invention is directed to an improvement in such pumps by the provision of a tubular diaphragm which is circular in cross-section at each of its end positions in the area of suction and discharge valves and which gradually transforms to an elliptical cross-section at its longitudinal mid-point while the internal circumference and wall thickness remain substantially constant.
As is well known, diaphragm pumps are especially useful for transporting viscous materials and corrosive fluids through pipes. In hydraulically actuated diaphragm pumps this is conventionally accomplished by means of a confined volume of hydraulic fluid exerting pressure on a diaphragm member. Check valves in these pumps limit the motion of the pumped or process material to a single direction so that the diaphragm acts as a positive displacement pump. Two diaphragms may be arranged in series, e.g., a flat diaphragm driving a tubular diaphragm through a coupling fluid, in order to isolate the pumped material from the hydraulic fluid and to permit optimization in the choice of diaphragm materials.
U.S. Pat. Nos. 2,345,693 and 3,318,251 show hydraulically actuated diaphragm pumps with a tubular diaphragm of uniform circular cross-section. However, it has been found that such diaphragms do not flex in any one predetermined direction upon compression. Predictability of the flex direction makes it possible to locate viewing ports in the pump head or casing to observe normal operation. In addition, viewing ports so located may be used to detect leakage of the process material or the working hydraulic fluid into the intermediate coupling fluid.
Oval or elliptical tubes have been proposed in pumps of the type shown in U.S. Pat. Nos. 2,046,491 and 3,451,347. Heretofore, such configurations have not been provided for the purpose of controlling the flex direction as the tubular diaphragm is compressed and relaxed. For example, the pumping system disclosed in U.S. Pat. No. 2,046,491 shows two oval tubes arranged one within the other and oriented so that their major axes are shifted 90.degree.. The direction of flex of the inner oval tube which pumps fuel is controlled by compression blocks actuated by the outer oval tube. The tubular diaphragm or chamber shown in U.S. Pat. No. 3,451,347 has an elliptical cross-section at the longitudinal mid-point but the inner circumference does not appear to remain constant.
Tubular diaphragm pumps known as "MILROYAL" and "mRoy TD" have been described in brochures of the Milton Roy Company in Ivyland, Pa. These pumps are described as having an elliptical tubular diaphragm but do not appear to taper gradually from a circular cross-section at each end to an elliptical cross-section at the longitudinal mid-point while maintaining a constant internal circumference. Instead, Bulletin 35.011 and Product Data brochure PD 15.30 show tubular diaphragms that neck down substantially at each end, thereby abruptly changing the inner circumference.